1. Field of the Invention
The present invention relates to a liquid crystal display device, a liquid crystal display method, a display control device, and a display control method. The present invention relates more specifically to a liquid crystal display device, a liquid crystal display method, a display control device, and a display control method that are capable of suppressing the occurrence of inconsistencies in the form of streaks without the size of a thin-film transistor (TFT) being increased.
2. Description of the Related Art
FIG. 1 shows a schematic diagram of an active matrix of a liquid crystal display panel used in, for example, liquid crystal televisions or the like. Here, four rows denoted by n through n+3 and four columns denoted by m through m+3 are shown. Although the pixel positioned at (n+1, m+3) is used as an example to describe constituent elements that constitute one of pixels, the constituent elements of each of the pixels of the liquid crystal panel are the same as those of the pixel positioned at (n+1, m+3), as a matter of course.
A pixel electrode is provided to each of the pixels that perform display, and a liquid crystal capacitor 11 is formed between the pixel electrode and a common electrode opposite the pixel electrode with liquid crystal therebetween. For each pixel electrode, a TFT 12 that functions as a switch is formed, a gate electrode of the TFT 12 is connected to a gate bus line 14, a source electrode of the TFT 12 is connected to a source bus line 13, and a drain electrode of the TFT 12 is connected to the pixel electrode.
Representative examples of a pattern of the polarity arrangement of pixels in a case where liquid crystal is driven will be described using FIGS. 2 and 3.
The pattern of the polarity arrangement shown in FIG. 2 is the most common, and is called dot inversion driving. In the pattern of the polarity arrangement, pixels of positive polarity and pixels of negative polarity are arranged in a checkerboard manner. In dot inversion driving, for example, pixels positioned at the top, the bottom, the right, and the left of a pixel of positive polarity at an arbitrary position have negative polarity. Similarly, pixels positioned at the top, the bottom, the right, and the left of a pixel of negative polarity at an arbitrary position have positive polarity. This pattern has an advantage in that even when the absolute value of the voltage of pixels of positive polarity and the absolute value of the voltage of pixels of negative polarity are not balanced because of inconsistencies in the common voltage, inconsistencies or flicker tends not to occur. However, in dot inversion driving, since the polarity of the output of a source bus line is inverted between positive and negative polarities in units of one line, there is a disadvantage in that the power consumption of a driver integrated circuit (IC) becomes large. In particular, when high-speed writing at 120 Hz or higher is performed in order to realize high-speed responsivity, this disadvantage becomes a severe problem.
Thus, at the time of high-speed driving, as shown in FIG. 3, vertical line inversion driving in which the polarity of pixels arranged in the vertical direction is not inverted within one frame is often performed (for example, see Japanese Unexamined Patent Application Publication No. 63-55590).
When liquid crystal driving is performed, it is ideal that the electric potential whose value is the center point between the positive and negative voltages applied to pixels is applied to the common electrode formed on the counter substrate, liquid crystal being provided between the pixel and common electrodes. When the value of a voltage applied to the common electrode has the central electric potential, the effective voltage applied to the liquid crystal is balanced in terms of positive and negative polarities and brightness does not vary between frames even when display is continuously performed at the same tone. However, it is significantly difficult to make the common voltage be optimal over the entire display unit because of various factors such as use of a transparent electrode ITO whose resistance is relatively high as the common electrode, the resistance of bus lines near TFTs, the parasitic capacitance of TFTs, TFT leakage, variations in liquid crystal capacitance. In this case, the effective voltage applied to a pixel of positive polarity is different from the effective voltage applied to a pixel of negative polarity pixel, and thus there is a problem in that the variations in brightness occur in units of one frame, that is, flicker occurs.
In dot inversion driving described using FIG. 2, positive and negative polarities are finely and evenly arranged in a mixed manner and the variations in brightness cancel each other out, whereby the degree of perception of flicker is greatly reduced. However, when vertical line inversion is employed, flicker occurs in the form of vertical streaks since positive polarities or negative polarities are continuously arranged in each vertical column.
The frequency at which flicker occurs is half the frequency of the driving frequency, and thus in the case of a normal driving frequency of 60 Hz, flicker occurs at a frequency of 30 Hz. Thus, the degree of perception of flicker is very high. In contrast, when the driving frequency becomes high such as 120 Hz or 240 Hz, flicker occurs at a frequency of 60 Hz or 120 Hz, whereby it is not perceived as flicker by the human eye. That is, even when vertical line inversion is employed, if display is performed at high frequencies, general flicker becomes unrecognizable.
In a VA mode, there is a disadvantage regarding the viewing-angle characteristics in halftones. In order to improve the viewing-angle characteristics in halftones, multi-pixel technology is widely used. FIG. 4 is a drawing illustrating a principle of a multi-pixel structure used for achieving a wide viewing angle in liquid crystal televisions and the like. A pixel is divided into two, for example, a sub-pixel A and a sub-pixel B. Regarding an input tone, the pixel is configured in such a manner that the brightness of the sub-pixel A first increases and-then the brightness of the sub-pixel B increases, and thus the entire brightness is adjusted so as to satisfy a gamma characteristic.
There are a plurality of ways to differentiate the electric potential of the sub-pixel A from the electric potential of the sub-pixel B. For example, a dedicated TFT is provided for each sub-pixel as shown in FIG. 5A and, as shown in an equivalent circuit of FIG. 5C, two source bus lines are provided for the same gate bus line using the pattern of the counter electrode ITO as shown in FIG. 5B. By driving TFTs for the sub-pixels A and B, the electric potential of the sub-pixel A can be differentiated from the electric potential of the sub-pixel B.
More specifically, in FIG. 5A, a pixel electrode for the sub-pixel A is denoted by Px1, and a pixel electrode for the sub-pixel B is denoted by Px2. A TFT for driving the pixel electrode Px1 is denoted by TFT1, and a TFT for driving the pixel electrode Px2 is denoted by TFT2. In the pixel electrodes Px1 and Px2, there are slits for inclining liquid crystal at an angle of 45 degrees, which is unique to the VA mode, and part of the slits are also used as slits for separating the pixel electrode Px1 from the pixel electrode Px2. Similarly, liquid-crystal orientation regulation means is necessary for the common electrode provided on the counter substrate. In FIG. 5A, the slits are indicated by broken lines, and the slits only for the counter electrode are shown in FIG. 5B. Here, an insulator protrusion may be formed on the common electrode as orientation regulation means. As shown in the equivalent circuit of FIG. 5C, the pixel electrodes Px1 and Px2 are electrically independent, and what voltages are to be applied to the pixel electrodes Px1 and Px2 are determined by a control circuit.